Add connectivity check through SOCKS5/HTTPS proxy

[cocakohler]

We sometimes need to check connectivity with customers that have strict security policies, e.g. connectivity to HTTPS or TCP endpoints is only allowed via SOCKS5 or a HTTP proxy.

• Check if SOCKS5 proxy is accessible
• Check if HTTPS connectivity is given through SOCKS5 proxy
• Check if TCP connectivity is given through SOCKS5 proxy
• Check if HTTPS proxy is accessible
• Check if HTTPS connectivity is given through HTTPS proxy